Air springs are increasingly utilized for suspension in passenger motor vehicles to increase the comfort of the suspension. An especially high level of suspension comfort is ensured when the air springs exhibit an excellent vibration characteristic over the entire vibration range. However, it has been shown that in air springs, which have a cylindrical flexible member, the suspension comfort is limited for small vibration amplitudes. The negative vibration characteristic is produced in that a hardening of the air spring occurs for small vibration amplitudes which limits the suspension comfort for these amplitudes.
Air springs have been developed which exhibit no spring hardening for small vibration amplitudes and therefore have an excellent vibration characteristic over the entire vibration range. The flexible member of such an air spring has, for example, a cylindrical form in the roll-off region thereof in order to facilitate an excellent roll off at large amplitudes of vibration. In contrast, the flexible member has in its chamber region, for example, the form of a barrel having a bulging mid portion. This barrel can then be slightly shortened under the action of a small force so that the air spring provides excellent suspension comfort even for small amplitudes of vibration. The cords are worked into the flexible member as a reinforcement. In the regions of different diameter, the cords assume different cord angles to the peripheral direction of the flexible member in order to make possible the above-described configuration of the air spring having different diameters in the longitudinal direction of the flexible member. The diameter of the flexible member, which is built into the air spring, is dependent upon the magnitude of the cord angle.
Published European patent application 0,285,726 (corresponds to U.S. patent application Ser. No. 032,212, filed Mar. 30, 1987) discloses air springs having a cord angle to the peripheral direction of the flexible member which is varied over the length thereof. The shape of the flexible member is influenced by the variation of the cord angle over the length of the flexible member. Especially air springs can be configured in the manner explained above.
The air springs disclosed in European patent publication 0,285,726 were produced in that the cords are wound individually into a flexible member disposed on a mandrel. For this purpose, the individual cords assume a specific angle to the mandrel and the mandrel is rotated about its longitudinal axis and is moved in longitudinal direction so that the individual cords are pulled into the flexible member at the specific angle. The desired variation of the angle of the cords takes place because of a variation of the speed of the mandrel in the longitudinal direction. Here, the angle of the embedded cords to the peripheral direction of the flexible member is that much greater the faster the mandrel moves in the longitudinal direction.
With the method disclosed in European patent publication 0,285,726, air springs can be made having flexible members wherein the cord angle varies in the longitudinal direction of the flexible member. However, it is necessary to wind several hundred cords into the flexible member of the air spring in order to impart a long service life and a high burst pressure thereto. However, this is only possible with great difficulty with the method known from the above-mentioned European patent publication because the cords must all be guided individually and this leads to problems when there is a high number of cords. Finally, processing errors can occur when the number of wound cords is too high and this can affect the quality of the finished air spring. In the known method, the number of wound-in cords is limited to a quantity which leads neither to a satisfactory service life nor to a satisfactory burst pressure.